The present invention relates generally to a device for spraying herbicides and more specifically to an agricultural chemical applicator for selectively applying herbicides and other chemicals to plants.
It will be appreciated by those skilled in the art that weeds and other unwanted plants grow in the same area as crops. These unwanted plants must be somehow removed or killed. Traditionally, these plants have been removed either manually, by spraying the entire field with a herbicide which will kill the unwanted plants but leave the wanted crops, or selectively applying herbicides to only those unwanted plants. Unfortunately, each of these methods, in the past, has tended to be highly labor intensive.
In the selective application of herbicides to the unwanted plants, growers have been required to apply the herbicides by hand. However, certain newer devices provide for selective spraying using various types of complicated sensors. Selective herbicides tend to be more expensive and cannot be economically applied to an entire field. Also, selective herbicides are not available for all crops.
One prior art attempt to address this issue is disclosed in U.S. Pat. No. 4,709,505 issued to B. Lempa, Jr. on Dec. 1, 1987. Lempa discloses a simple device which provides a valve connected to a tank by a hose. An arm extends downwardly which, when the arm catches on a plant, opens the valve which causes spraying. Unfortunately, this device is not easily adjustable. Also, the long extending rod which is necessary to form the moment arm which allows a plant to open up a valve requires that the unwanted plants extending beyond the crops be very low to the ground but be significantly above the wanted crops.
A more complicated device for selective spraying of plants disclosed in U.S. Pat. No. 4,991,341, issued to B. Douglas on Feb. 12, 1991. This particular device uses a sensor such as an ultrasonic transducer to scan a certain area. The device also has a ground sensor which determines the speed of the tractor determine the amount of herbicide to be applied. Unfortunately, each of these designs requires a computer and complex optics.
Another simple method is disclosed in U.S. Pat. No. 4,187,638 issued to J. Hardy et al. on Feb. 12, 1980. In this particular embodiment, an elongated reservoir for a chemical is provided having wicks extending axially along the outside of the container. A chemical is absorbed within the wick. As plants contact the wick, the chemical is applied to the plants. Unfortunately, the amount of herbicide which is provided by the wick is very limited and difficult to control with precision.
The December 1991 issue of Farm Journal discusses generally two other types of sprayers. Each uses a type of sensor which scans a certain area. Each of the sensors apparently is an optic sensor. The optic sensors tend to be much more complex than are really necessary. The complexity adds to the cost of the overall device.
One characteristic of weed growth that is of benefit in the selective application of either a selective or non-selective herbicide is the tendency of weeds in certain crops to grow faster than the crops. Thus, early in the growing season, when crops are short, a direct application of a selective herbicide to weed foliage can be accomplished with good results, if equipment were available to detect the taller weeds and apply the herbicide in response.
What is needed, then, is a device for the selective spraying of herbicides which is not complex. The needed sprayer must be able to differentiate the crop canopy from the unwanted weeds. The device must be able to selectively apply herbicides in such a manner so as not to waste herbicides, while at the same time providing enough herbicide to kill the unwanted plants. The device must selectively spray herbicides so as to use less herbicide to kill the unwanted plants. This device is presently lacking in the prior art.